A person's mobility depends on an adaptively functioning perception-action system. Consequently, mobility limitations can arise from a host of pathologies and injuries that affect various loci in this system, from sensory receptors to cortical areas to musculo-skeletal components. However, such deficits typically impact the function of the system as a whole, and require adaption of perceptual-motor control strategies. For example, a chronic knee injury may alter the actions afforded by the environment and require the remapping of visual information to gait control variables in order to generate adaptive locomotion. Rehabilitation may thus not only involve strengthening muscles and retraining motor patterns, but relearning whole perceptual-motor control relations.
Mobility deficits may persist indefinitely and often deteriorate over time. For instance, at 12 months post-stroke, patients suffering from hemiplegia may exhibit motor deficits in the form of longer gait cycles with decreased cadences, and may result in a 50% reduction in walking speed compared to the gait patterns of unaffected control participants (Olney & Richards, Gait Posture 4: 136-138, 1996; von Schroeder, Coutts, Lyden, Billings, & Nickel, J Rehabil Res Dev. 32: 25-31, 1995). In another example, patients suffering from Parkinson's disease frequently exhibit freezing gait—a term that encompasses both the inability of the patient to initiate or sustain a walking gait, and shuffling forward with small steps as their legs exhibit muscle trembling—and these symptoms worsen as the disease progresses (Bloem, Hausdorff, Visser & Giladi, Move Disord. 19: 871-84, 2004; Riess, Ios Press, 200-208, 1998). Mobility issues are also the typical sequelae of sensory deficits such as “tunnel vision” due to conditions like retinitis pigmentosa (RP)—a group of hereditary disorders characterized by retinal pigmentary degeneration that often leads to progressive visual field loss (Geruschat, Turano & Stahl, Optom Vis Sci. 75:525-37, 1998; Haymes, Guest, Heyes & Johnston, Optom Vis Sci. 73:621-37, 1996; Kuyk, Elliott, Biehl & Fuhr, J Am Optom Assoc. 67: 403-9, 1996; Lovie-Kitchin, Mainstone, Robinson & Brown, Clin Vis Sci 5:249-263, 1990; Turano, Geruschat, Baker, Stahl, & Shapiro, Optom Vis Sci. 78:667-75, 2001).
This spectrum of deficits may detract from a patient's functional mobility by reducing their ability to adapt (prospectively and/or reactively) to normally varying environmental conditions during locomotion. Moreover, the basis of these deficits directly impacts the type and severity of such deficits, as well as the type of interventions that can be utilized to improve patient mobility. In direct response to these problems, researchers have started to employ virtual reality (VR) training interventions that may facilitate rehab of patients with mobility deficits.
The advent of VR as a tool for real-world training dates back to the mid-twentieth century and the early years of driving and flight simulators. These simulation environments, while far below the quality of today's visual displays, proved to be advantageous to the learner due to the safe training environments the simulations provided. More recently, these training environments have proven beneficial in the transferability of user-learned skills from the simulated environment to the real world. The development of VR technology of today has included, for example, contemporary displays boasting higher quality resolutions, wide-angle field of views and increased portability. This has led to the evolution of new VR research and training applications in many different arenas. This is true of clinical assessment and rehabilitation, as the field has recognized some potential advantages of incorporating VR technologies into patient training Unfortunately, many of the early desktop VR clinical interventions suffer from technological constraints in hardware and software that may limit their value as training tools for many clinical populations.
One of the major challenges facing VR-based assessment and rehabilitation is determining the type of VR installation to employ. This may require a greater understanding of the parameters needed to measure and/or access any locomotor deficiencies in patients in order to fully appreciate any defects and to treat the same. The hardware, such as visual displays and head tracking devices available, as well as systems for kinematic and kinetic measurement of movement, may strongly constrain the type of locomotor behavior permitted. For example, while over-ground walking may allow for the most natural interaction between the user and a virtual environment, space limitations may physically limit traditional systems.
Accordingly, a need exists for developing and refining new technological advancements to provide enhanced training tools that allow a user to navigate virtual environments. A need further exists to provided combined and improved visual displays, which serve to enhance the immersive nature of VR and efforts to introduce new behavioral measurement opportunities to facilitate the rehabilitation of patients.